NMEA VLW datagram format
The NMEA VLW datagram contains the travelled distance of the vessel. Two values are provided; relative to the water and over the ground.
Format
$--VLW,x.x,N,y.y,N,z.z,N,g.g,N*hh<CR><LF>
Description
1 $—Talker identifier
2 VLWDatagram identifier
3 x.x,NDistance relative to waterTotal cumulative (nautical miles)
4 y.y,NDistance relative to waterSince reset (nautical miles)
5 z.z,NDistance relative to groundTotal cumulative (nautical miles)
6 g.g,NDistance relative to groundSince reset (nautical miles)
7 *hhChecksum